This invention relates to a method and apparatus for the collection and subsequent regeneration and recovery of substances exhausted through a vacuum pump and, more particularly, of condensible substances including solvents.
Numerous processes are known requiring the evacuation or extraction of a variety of chemical compounds, many of which are volatile, by vacuum pump means and which require to be collected and recovered for economic or environmental reasons.
It is, for example, known to pass exhaust stream from a vacuum pump to pressure swing adsorption (PSA) apparatus in which one or more beds of activated carbon, molecular sieve material or zeolite material adsorbs one or more components of the exhaust stream including solvents and a variety of volatile organic compounds.
Regeneration of the adsorption beds can generally be accomplished, especially in the case of solvents, by
i) heating the bed with nitrogen gas so that the desorbed solvent is, at reduced pressure, entrained in the nitrogen stream and thereafter passing the stream through a liquid nitrogen condenser to remove the solvent and feeding the nitrogen back into the bed following reheating; or PA0 ii) heating the bed directly by, for example, embedded heating coils, indirect heating means or heat transfer coils and subjecting the bed to vacuum, whereby desorbed solvent can be pumped away and condensed.
There are, however, difficulties in connection with the known methods described above. In particular, it is clear that liquid nitrogen and/or an additional vacuum pump has to be provided; even then the additional pump may itself produce an emission of exhaust stream components which may themselves have to be scrubbed. In addition, for adsorbent heating during regeneration, some additional energy source has to be provided. In all such cases additional capital costs and/or operating costs are therefore required.
The present invention is, however, concerned with the provision of an improved collection/recovery method in which no liquid or gaseous nitrogen is required and no additional vacuum pump, additional heating means or other energy source is required.